In the rodent there are two isoforms of the GH receptor derived from the same gene. The long form GHRL spans the cell membrane and can signal most if not all of the effects of GH probably through activation of the cytosolic protein tyrosine kinase, JAK2. The short isoform of the receptor, GHRs consists only of the extracellular domain and a hydrophilic tail, but is somehow tethered to the cell surface where it participates in hormone binding and probably signaling. Dr. Goodman will examine the effects of the influx of ca2+ brought on by GH on the expression of the above effects and in particular the refractory response. The role of Ca2+ and its potential second messenger function as a modulator or director of the signaling cascades initiated by tyrosine phosphorylation of cellular proteins will be explored.